1. Technical Field of the Invention
The embodiments of the invention relate generally to disk drives and, more particularly, to a use of ECC in combination with iterative decoding.
2. Description of Related Art
Varieties of memory storage devices, such as magnetic disk drives, are available to store data and are used to provide data storage for a host device, either directly, or through a network. Those networks may be a storage area network (SAN) or a network attached storage (NAS). Typical host devices include stand alone computer systems such as a desktop or laptop computer, enterprise storage devices such as servers, storage arrays such as a redundant array of independent disk (RAID) arrays, storage routers, storage switches and storage directors, and other consumer devices such as video game systems and digital video recorders. These devices generally provide high storage capacity in a cost effective manner. Disk drives, including hard disk drives (HDDs), comprise one category of such storage devices.
With some of the HDDs, there may be performance issues associated when performing timing recovery of a signal that is read from the disk. That is, appropriate digital sampling is performed for accurate and effective recovery of the information from signals read from the disk. If improper or inadequate digital sampling is performed on the signal that is read from the disk, then some of the data recovered may be inaccurate or not recovered at all.
In order to continually improve the data read capabilities of HDDs, various sampling techniques may be implemented or enhanced to read, sample and recover the stored data. However, one limiting factor with HDDs is the standard that is implemented with the disk operating system in setting a particular sector size for HDDs. For example, personal computers operating on Microsoft Corporation's current operating system software partition HDDs into 512 byte sectors. Thus, 512 byte sector size is a standard that is used with computers utilizing this operating system.
In the future, operating system software may partition the HDD to have larger sector sizes. For example, one upgraded operating system may partitioned the disk into 4096 (4K) byte sector size. In this instance, there is an eight-fold increase in the sector size. In response, corresponding changes in circuitry and sampling techniques will most likely be needed to accommodate the larger sector size. It is appreciated that until the larger sector size (for example, the 4K byte sector size) becomes prevalent, computer systems may still operate with HDDs that have currently existing sector size, such as the 512 byte sector size. The term used to describe current and past implementation is generally referred to as “legacy.”
Accordingly, for an interim time period, manufacturers of HDDs may be required to provide HDDs that operate at 512 byte sector size HDDs, as well as 4K byte sector size HDDs. However, certain circuitry allowing for an acceptable bit error rate (BER) for 512 byte sectors may not provide acceptable BER at the larger sector size, since parameters that affect the BER at one sector size may have significantly different characteristics at a second sector size. Therefore, HDD devices or controllers that control a hard disk may be required to provide separate circuitry to handle each of the sector sizes being implemented or alternatively, provide HDDs or controllers that is operable with one selected sector size.
For manufacturers of integrated circuits (ICs) that operate as controllers to control a HDD, two choices are available to decode the sampled data at two different sector sizes. One is to manufacture separate ICs for each of the sector sizes to handle the differences in decoding. However, this results in two separate IC designs, one for each type of IC. The disadvantage of this approach is that the legacy design (e.g. 512 byte sectors) is operable only with the legacy HDD (e.g. HDDs capable of 512 byte sectors only). Thus, if a legacy HDD controller is present in a computer system operating with the legacy operating system, when the computer system is upgraded to the new operating system capable of using the larger sector size, the HDD may need to be replaced.
A second choice is to include separate circuitry for each different sector size in the one IC, and allow the HDD to migrate to the large sector size. This allows one IC design to operate with both sector sizes, so that the controller IC chip and/or the HDD, need not be made obsolete when migrating to the new operating system (or other software) that uses the larger sector size.